1897 THE MICROSCOPE. 55 
it for only a short time, rarely as long as five minutes, 
except in the case of Perenyis, when two hours is better. 
They are then to be placed into 50 per cent alcohol, which 
should be changed once or twice, for afew hours; then 
into 70 per cent for a day; finally into 80 per cent, which 
seems to be the best strength for final preservation. It 
is well to change this after a few days. 
CAMPANULARIAN Hyprorpbs.-—These in general form 
and habitat are like the preceding, differing however in 
a number of important details. The accompanying 
figure (6) will serve to show the special differences in 
structure. It will be noticed at once that these animals 
are encased by a horny covering, the perisarc, which 
about the head is bell-shaped, thus the name campanu- 
larian. 
The method of giving rise to the jelly-fish is charac- 
teristic, and occurs in the club-shaped gonotheea (fig. 6. go.) 
which consists essentially of an axis from which the 
meduse bud, the whole being protected by acase. Here 
again we find the degenerated form of retaining the 
medusa, allowing the egg development to proceed until 
the planule are produced. It is easy, on keeping 
hydroids during the reproductive season, to find in the 
water either those dainty little swimming je!ly-fishes, or 
the white worm-like planula. The latter when examined 
with the microscape, are seen to be a little solid cellular 
mass, consisting of two kind of cells, an outer layer form- 
ing the ectoderm, the inner consisting of the endodermal 
“cells, which as development proceeds separate, forming a 
central cavity which, by and by becomes the stomach. 
The outer surface of the ectodermal cells is richly pro- 
vided with cilia, by which the animal moves. The com- 
plete development into the adult hydroid 1s easily studied 
and occupies but a few days. 
PRESERVATION.—The method outlined for the tubu- 
larians, will preserve these excellently for histological 
